Question about Motronic 2.9 fuel mileage signal

Does anyone know what kind of signal the Corrado VR6 ECU (Motronic 2.9) outputs for the fuel mileage signal to the instrument cluster? I'm wondering if it a varying voltage that is proportional to the fuel used, or if it is a pulse frequency for when the injectors fire and the MFA does some rough calculation to estimate the fuel used. Thanks.